在 R 中有条件地提取向量名称

Question

I'm trying to get the names of the elements in a vector with some priorities.

If there is any element with value "integer" , get the name of the first of such elements (in the example below, year )

But if there is no element with value "integer" , then do the same thing with any element with value "numeric" .

I have tried the following without success ( this is a toy example a functional answer is appreciated ):

cl <- c(group = "character", degree = "numeric", year = "integer", zoo = "integer")

names(cl[cl == "integer" || cl == "numeric"])[1]

desired.output = "year"

Answer 1

You're close, but there are two issues with your approach so far:

1. The || operator only works with one element; since you're looking over more than one you would want | instead. See ?`||` for more details.
2. Your approach would treat "integer" and "numeric" equally, rather than prioritising numeric as you would prefer.

One way of doing it would be:

Coalesce2 <- function(x, y) if(is.na(x))  y  else  x
Coalesce2(cl[cl == "integer"][1], cl[cl == "numeric"][1])

NB. The only reason I've made a new coalesce function here rather than using dplyr's is that that doesn't preserve names in the way I think you want.

Answer 2

As it is a fixed match, we can use %in%

names(sort(cl[cl %in% c('integer', 'numeric')]))[1]
#[1] "year"

---

Or convert to factor with levels specified

names(sort(factor(cl, c('integer', 'numeric'))))[1]
#[1] "year"

---

Or with match

names(cl)[na.omit(match(c('integer', 'numeric'), cl))[1]]
#[1] "year"

Answer 3

Using grep .

names(sort(cl[grep("integer|numeric", cl)])[1])
# [1] "year"